1. Field of the Invention
The present invention relates to communication schemes for machines, and, more particularly, to communication schemes for wind turbines.
2. Description of the Related Art
Harvesting wind energy via wind turbines to supply electrical power is an increasing market. On a pitch controlled wind turbine, the electronic controller of the turbine checks the power output of the turbine multiple times per second. When the power output becomes too high, the electronic controller sends a command to the blade pitch actuator which immediately pitches (turns or rotates) the rotor blades slightly out of the wind (i.e., so the face of the blade is not so nearly perpendicular to the wind direction). Conversely, the blades are turned back into the wind (i.e. so the face of the blade is more perpendicular to the wind direction) whenever the wind drops again. Thus, the rotor blades have to be able to rotate about their longitudinal axis in order to pitch.
During normal operation the blades may pitch less than one degree at a time, all while the rotor is turning. A pitch controlled, or “variable pitch” wind turbine may typically be designed such that the rotor blades pitch exactly the desired amount. On a pitch controlled wind turbine, the central controller may pitch the blades a few degrees each time the wind changes to thereby maintain the rotor blades at an optimum angle and maximize power output for all wind speeds. The actuator for changing the pitch is usually hydraulic.
The rotor blades of the turbine are typically designed with maximum length and minimum size in order to increase efficiency, which, however, also subjects the blades to relatively high deflection forces. Such deflection forces may cause fatigue and eventually failure in the blades and other wind turbine components. Thus, deflection should be sensed, controlled and minimized. For example, if the amount of deflection becomes too great, then the central controller may send a command to the hydraulic actuator to change the pitch such that the blade faces more away from the wind.
In order to monitor the condition of wind turbines, including the amount of deflection of the blades, sensors can be installed on the rotor blades. These sensors need to communicate with a central controller which is normally located in the tower of the wind turbine. The sensors communicate with the central controller via wired connections. The electrical connection between the rotating blade and the stationary tower may be achieved with the use of slip rings.
There are problems associated with the use of slip rings, however. First, slip rings are a relatively expensive type of electrical connector because they must be designed to withstand nearly continuous motion of their components relative to each other. Second, despite the relatively high level of engineering that goes into the design of slip rings, they may have a higher rate of failure than other types of electrical connectors because of the constant motion and mechanical forces to which they are subjected during operation. Third, the use of a slip ring in a wind turbine increases the susceptibility to lightning strikes because lightning that hits a blade of the wind turbine may be carried to the central unit in the tower via the slip ring.
What is neither disclosed nor suggested in the art is an electrical communication scheme for a wind turbine that does not require the use of a slip ring with its associated problems and limitations as described above.